Phase based distance estimation with carrier frequency offset

ABSTRACT

A transceiver circuit is disclosed. The transceiver circuit includes an antenna, a receiver RF chain configured to receive a receiver RF signal from the antenna, a transmitter RF chain configured to transmit a transmitter RF signal to the antenna, and a controller configured to access a CFO (carrier frequency offset) estimate, and to, for each of one or more working frequencies: cause the receiver RF chain to receive a receiver RF signal from the antenna at each working frequency, generate I/Q measurement data based at least in part on the received receiver RF signal and the CFO estimate, store the I/Q measurement data, and cause the transmitter RF chain to transmit a transmitter RF signal to the antenna at each working frequency, where the controller is further configured to cause the transmitter RF chain to transmit the I/Q measurement data for each working frequency to the antenna.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/491,499, titled “PHASE BASED DISTANCE ESTIMATION WITH CARRIERFREQUENCY OFFSET,” filed Sep. 30, 2021, which is hereby incorporated inits entirety and for all purposes.

TECHNICAL FIELD

The subject matter described herein relates to determining a distance(ranging) between two transceivers, and more particularly to determiningthe distance in the presence of carrier frequency offset (CFO).

BACKGROUND

Distances between two communicating transceivers are increasingly usedfor various applications. For example, various Bluetooth Low Energy(BLE) and internet of things (IOT) applications require accuratedistance measurements. Various distance measurement or rangingtechniques are used to determine the distances between transceivers. Ofthese, phase-based ranging techniques are of increasing interest.Techniques for accurately calculating distances between transceivers inthe presence of CFO are needed in the art.

SUMMARY

One inventive aspect is a transceiver circuit, including an antenna, areceiver RF chain configured to receive a receiver RF signal from theantenna, a transmitter RF chain configured to transmit a transmitter RFsignal to the antenna, and a controller configured to access a CFO(carrier frequency offset) estimate, and to, for each of one or moreworking frequencies: cause the transmitter RF chain to transmit atransmitter RF signal to the antenna at each working frequency, causethe receiver RF chain to receive a receiver RF signal from the antennaat each working frequency, and generate first I/Q measurement data basedat least in part on the received receiver RF signal and the CFOestimate. In some embodiments, the controller is further configured tocause the receiver RF chain to receive I/Q measurement information foreach working frequency from the antenna. In some embodiments, thecontroller is further configured to generate second I/Q measurement databased at least in part on the received I/Q measurement information. Insome embodiments, the controller is further configured to estimate adistance between the antenna and an antenna of another device based atleast in part on the first and second I/Q measurement data.

In some embodiments, the transceiver circuit further includes afrequency synthesizer configured to control the working frequency. Insome embodiments, the controller is configured to cause the frequencysynthesizer to set the working frequency to a particular workingfrequency before causing the transmitter RF chain to transmit aparticular transmitter RF signal to the antenna at the particularworking frequency. In some embodiments, the controller is configured tocause the frequency synthesizer to maintain the working frequency at thea particular working frequency at least until the controller causes thereceiver RF chain to receive a particular receiver RF signal from theantenna at the particular working frequency.

In some embodiments, the transceiver circuit further includes afrequency synthesizer configured to control the working frequency. Insome embodiments, the controller is configured to cause the frequencysynthesizer to set the working frequency to a particular workingfrequency before causing the receiver RF chain to receive a particularreceiver RF signal from the antenna at the particular working frequency.In some embodiments, the controller is configured to cause the frequencysynthesizer to maintain the working frequency at the a particularworking frequency at least until the controller causes the transmitterRF chain to transmit a particular transmitter RF signal to the antennaat the particular working frequency.

In some embodiments, the controller is further configured to cause thereceiver RF chain to receive a CFO RF signal from the antenna at apredetermined working frequency, and to generate the CFO estimate basedat least in part on I/Q measurement data of the CFO RF signal.

In some embodiments, the one or more working frequencies includes aplurality of working frequencies spanning a frequency band of interest.In some embodiments, the predetermined working frequency is about in themiddle of the frequency band of interest.

In some embodiments, the one or more working frequencies includes firstand second working frequencies. In some embodiments, the first I/Qmeasurement data generated based in part on the receiver RF signalsreceived at each of the first and second working frequencies aregenerated based in part on the same CFO estimate.

In some embodiments, the one or more working frequencies includes aplurality of working frequencies. In some embodiments, all of the firstI/Q measurement data generated based on the received receiver RF signalswhich the distance is estimated based on, is generated based on the sameCFO estimate.

In some embodiments, all of the I/Q measurement information used togenerate the second I/Q measurement data is generated based on the sameCFO estimate.

In some embodiments, the second I/Q measurement data is generated basedin part on the same CFO estimate.

Another inventive aspect is a transceiver circuit, including an antenna,a receiver RF chain configured to receive a receiver RF signal from theantenna, a transmitter RF chain configured to transmit a transmitter RFsignal to the antenna, and a controller configured to access a CFO(carrier frequency offset) estimate, and to, for each of one or moreworking frequencies: cause the receiver RF chain to receive a receiverRF signal from the antenna at each working frequency, generate I/Qmeasurement data based at least in part on the received receiver RFsignal and the CFO estimate, store the I/Q measurement data, and causethe transmitter RF chain to transmit a transmitter RF signal to theantenna at each working frequency. In some embodiments, the controlleris further configured to cause the transmitter RF chain to transmit theI/Q measurement data for each working frequency to the antenna.

In some embodiments, the transceiver circuit further includes afrequency synthesizer configured to control the working frequency. Insome embodiments, the controller is configured to cause the frequencysynthesizer to set the working frequency to a particular workingfrequency before causing the receiver RF chain to receive a particularreceiver RF signal from the antenna at the particular working frequency.In some embodiments, the controller is configured to cause the frequencysynthesizer to maintain the working frequency at the a particularworking frequency at least until the controller causes the transmitterRF chain to transmit a particular transmitter RF signal to the antennaat the particular working frequency.

In some embodiments, the transceiver circuit further includes afrequency synthesizer configured to control the working frequency. Insome embodiments, the controller is configured to cause the frequencysynthesizer to set the working frequency to a particular workingfrequency before causing the transmitter RF chain to transmit aparticular transmitter RF signal to the antenna at the particularworking frequency. In some embodiments, the controller is configured tocause the frequency synthesizer to maintain the working frequency at thea particular working frequency at least until the controller causes thereceiver RF chain to receive a particular receiver RF signal from theantenna at the particular working frequency.

In some embodiments, the controller is further configured to cause thereceiver RF chain to receive a CFO RF signal from the antenna at apredetermined working frequency, and to generate the CFO estimate basedat least in part on I/Q measurement data of the CFO RF signal.

In some embodiments, the one or more working frequencies includes aplurality of working frequencies spanning a frequency band of interest.In some embodiments, the predetermined working frequency is about in themiddle of the frequency band of interest.

In some embodiments, the one or more working frequencies includes firstand second working frequencies. In some embodiments, the I/Q measurementdata generated based in part on the receiver RF signals received at eachof the first and second working frequencies are generated based in parton the same CFO estimate.

In some embodiments, the one or more working frequencies includes aplurality of working frequencies. In some embodiments, all of the I/Qmeasurement data transmitted for each working frequency is generatedbased on the same CFO estimate.

Another inventive aspect is a transceiver circuit, including an antenna,a receiver RF chain configured to receive a receiver RF signal from theantenna, a transmitter RF chain configured to transmit a transmitter RFsignal to the antenna, and a controller configured to, for each of oneor more working frequencies: cause the transmitter RF chain to transmita transmitter RF signal to the antenna at each working frequency, causethe receiver RF chain to receive a receiver RF signal from the antennaat each working frequency, generate a communication CFO estimate basedat least in part on the received receiver RF signal, and generate firstI/Q measurement data based at least in part on the received receiver RFsignal and the generated communication CFO estimate. In someembodiments, the controller is further configured to cause the receiverRF chain to receive I/Q measurement information for each workingfrequency from the antenna. In some embodiments, the controller isfurther configured to generate second I/Q measurement data based atleast in part on the received I/Q measurement information. In someembodiments, the controller is further configured to access a single CFOestimate. In some embodiments, the controller is further configured torevise the first and second FQ measurement data such that the revisedfirst and second I/Q measurement data is generated based on the singleCFO estimate. In some embodiments, the controller is further configuredto estimate a distance between the antenna and an antenna of anotherdevice based at least in part on the revised first and second I/Qmeasurement data.

In some embodiments, the transceiver circuit further includes afrequency synthesizer configured to control the working frequency. Insome embodiments, the controller is configured to cause the cause thefrequency synthesizer to set the working frequency to a particularworking frequency before causing the transmitter RF chain to transmit aparticular transmitter RF signal to the antenna at the particularworking frequency. In some embodiments, the controller is configured tocause the frequency synthesizer to maintain the working frequency at thea particular working frequency at least until the controller causes thereceiver RF chain to receive a particular receiver RF signal from theantenna at the particular working frequency.

In some embodiments, the controller is further configured to revise thefirst I/Q measurement data by removing an effect of the communicationCFO estimate from the first and second I/Q measurement data.

In some embodiments, the controller is further configured to revise thefirst and second I/Q measurement data by including an effect of thesingle CFO estimate on the first and second I/Q measurement data.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations.

FIG. 1A is a schematic diagram of an embodiment of a transmitter circuitaccording to some embodiments.

FIG. 1B is a schematic diagram of an embodiment of a receiver circuitaccording to some embodiments.

FIG. 2 is a schematic diagram of an embodiment of a transceiver circuitaccording to some embodiments.

FIG. 3 is schematic diagram of first and second transceiverscommunicating wirelessly.

FIG. 4 is a flowchart diagram illustrating a method of determining adistance between first and second transceivers according to someembodiments.

FIG. 5 is a schematic diagram representing the actions of the first andsecond transceivers performing certain portions of the method of FIG. 4according to some embodiments.

FIG. 6 is a flowchart diagram illustrating a method of determining adistance between first and second transceivers according to someembodiments.

FIG. 7 is a schematic diagram representing the actions of the first andsecond transceivers performing certain portions of the method of FIG. 6according to some embodiments.

FIG. 8 is a flowchart diagram illustrating a method of determining adistance between first and second transceivers according to someembodiments.

When practical, similar reference numbers denote similar structures,features, or elements.

DETAILED DESCRIPTION

Particular embodiments of the invention are illustrated herein inconjunction with the drawings.

Various details are set forth herein as they relate to certainembodiments. However, the invention can also be implemented in wayswhich are different from those described herein. Modifications can bemade to the discussed embodiments by those skilled in the art withoutdeparting from the invention. Therefore, the invention is not limited toparticular embodiments disclosed herein.

Embodiments illustrate circuits and methods for determining a distancebetween first and second transceivers. The distances are determinedusing phased based methods in the presence of CFO. The distances arecalculated using techniques which account for the CFO. FIGS. 1A and 1Brespectively illustrate schematic diagrams of a receiver circuit and atransmitter circuit. FIG. 2 is a schematic diagram of an embodiment of atransceiver circuit according to some embodiments. FIGS. 3-8 areschematic diagrams and flowchart diagrams illustrating methods ofdetermining a distance between first and second transceivers accordingto some embodiments.

FIG. 1A is a schematic diagram of an embodiment of a transmitter circuit100 according to an embodiment. Transmitter circuit 100 includes antennaor antenna array 110, switch 120, RF chain 130, and controller 140.Transmitter circuit 100 illustrates a particular example. Otherembodiments of transmitter circuits may be used.

Antenna or antenna array 110 may be any antenna or antenna array. Forexample, in some embodiments, antenna or antenna array 110 includes 1,2, 3, 4, or more antennas. In some embodiments, antenna or antenna array110 includes a linear antenna array. In some embodiments, antenna orantenna array 110 includes a two dimensional antenna array, for example,having multiple rows of linear antenna arrays.

In embodiments where antenna or antenna array 110 includes one antenna,the one antenna may be connected directly to RF chain 130, and switch120 may be omitted. In embodiments where antenna or antenna array 110includes multiple antennas, each antenna may be directly connected to aseparate RF chain. Each of the RF chains may have the features of RFchain 130.

Antenna or antenna array 110 may be configured to transmit RF signals toa receiver circuit, such as receiver circuit 200 described below withreference to FIG. 1B. The RF signals include a high frequency signal ata carrier frequency modulated with a low frequency information signal.The high frequency signal is transmitted by one of the antennas fromantenna or antenna array 110, for example, according to a programmableelectrical connection formed by switch 120, as controlled by controller140.

Controller 140 is configured to provide a digital signal to RF chain130, where the digital signal encodes the information signal to betransmitted by antenna or antenna array 110.

RF chain 130 includes digital to analog converter (DAC) 132, mixer 136,frequency synthesizer 134, and power amplifier (PA) 138. RF chain 130 isan example only, and embodiments of other RF chains may alternatively beused. For example, in some embodiments, one or more amplifiers, and/orfilters may be included, as understood by those of skill in the art.

The digital signal is processed by the digital to analog converter 132to generate an analog baseband signal (BB signal) representing thedigital signal, using techniques known in the art. Various digital toanalog converter structures known in the art may be used.

Mixer 136 receives the analog baseband signal output from the digital toanalog converter 132 and an oscillator signal at the carrier frequencygenerated by frequency synthesizer 134. In response to the analogbaseband signal and the oscillator signal, mixer 136 up converts theanalog baseband signal from the analog-to-digital converter 132 to ahigh frequency signal, using techniques known in the art. Various mixerstructures known in the art may be used. The resulting high frequencysignal is at the carrier frequency in this modulated so as to includethe information of the low frequency information signal.

Power amplifier 138 is configured to receive the high frequency signaland to drive the high frequency signal to one of the antennas fromantenna or antenna array 110, for example, according to a programmableelectrical connection formed by switch 120, as controlled by controller140. The power amplifier 138 drives the high frequency signal to one ofthe antennas using techniques known in the art. Various power amplifierstructures known in the art may be used.

As understood by those of skill in the art, using communicationconnectivity not illustrated in FIG. 1A, control signals from controller140 may control certain variable functionality of switch 120, poweramplifier 138, frequency synthesizer 134, mixer 136, and digital toanalog converter 132, for example, as understood by those of skill inthe art.

The control signals from controller 140 may, for example, control switch120 to control which of multiple antennas RF chain 130 drives the highfrequency signal with.

In embodiments having multiple antennas each connected to one ofmultiple RF chains, controller 140 may generate control signals for eachof the RF chains.

FIG. 1B is a schematic diagram of an embodiment of a receiver circuit200 according to an embodiment. Receiver circuit 200 includes antenna orantenna array 210, switch 220, RF chain 230, and controller 240.Receiver circuit 200 illustrates a particular example. Other embodimentsof receiver circuits may be used.

Antenna or antenna array 210 may be any antenna or antenna array. Forexample, in some embodiments, antenna or antenna array 210 includes 1,2, 3, 4, or more antennas. In some embodiments, antenna or antenna array210 includes a linear antenna array. In some embodiments, antenna orantenna array 210 includes a two dimensional antenna array, for example,having multiple rows of linear antenna arrays.

In embodiments where antenna or antenna array 210 includes one antenna,the one antenna may be connected directly to RF chain 230, and switch220 may be omitted. In embodiments where antenna or antenna array 210includes multiple antennas, each antenna may be directly connected to aseparate RF chain. Each of the RF chains may have the features of RFchain 230.

Antenna or antenna array 210 may be configured to receive RF signalsgenerated by a transmitter, such as transmitter 100 described above withreference to FIG. 1A.

RF chain 230 includes low noise amplifier (LNA) 232, frequencysynthesizer 234, mixer 236, and analog to digital converter (ADC) 238.RF chain 230 is an example only, and embodiments of other RF chains mayalternatively be used. For example, in some embodiments, one or moreamplifiers, and/or filters may be included, as understood by those ofskill in the art.

Low noise amplifier 232 is configured to receive a high frequency signalat a carrier frequency and modulated with a low frequency informationsignal. The high frequency signal is received from one of the antennasfrom antenna or antenna array 210, for example, according to aprogrammable electrical connection formed by switch 220, as controlledby controller 240. The high frequency signal is amplified by low noiseamplifier 232 to generate an amplified RF signal, using techniques knownin the art. Various low noise amplifier structures known in the art maybe used.

Mixer 236 receives the amplified RF signal output from the low noiseamplifier 232 and an oscillator signal at or substantially at thecarrier frequency generated by frequency synthesizer 234. In response tothe amplified RF signal and the oscillator signal, mixer 236 downconverts the amplified RF signal from the low noise amplifier 232 to abaseband signal, using techniques known in the art. Various mixerstructures known in the art may be used. The resulting baseband signalincludes information of the low frequency information signal.

The baseband signal is then processed by the analog-to-digital converter238 to generate a digital signal representing the baseband signal, usingtechniques known in the art. Various analog-to-digital converterstructures known in the art may be used.

Controller 240 receives the digital representation of the basebandsignal.

As understood by those of skill in the art, using communicationconnectivity not illustrated in FIG. 1B, control signals from controller240 may control certain variable functionality of switch 220, low noiseamplifier 232, frequency synthesizer 234, mixer 236, andanalog-to-digital converter 238, for example, as understood by those ofskill in the art.

The control signals from controller 240 may, for example, control switch220 to select which of multiple antennas RF chain 230 receives the highfrequency signals from.

For example, controller 240 may generate control signals which result incontroller 240 receiving a group of digital signals, where each digitalsignal of the group is generated by RF chain 230 based on a highfrequency signal received by a selected one of the antennas. Inembodiments having multiple antennas each connected to one of multipleRF chains, controller 240 may generate control signals for each of theRF chains, such that controller 240 receives a group of digital signals,where each digital signal of the group is generated by one of the RFchains based on an RF signal received by the particular antennaconnected thereto.

FIG. 2 is a schematic diagram of an embodiment of a transceiver circuit300 according to some embodiments. Transceiver circuit 300 includesantenna or antenna array 110, switch 120, receiver RF chain 130,transmitter RF chain 230, and controller 140. Transceiver circuit 300illustrates a particular example. Other embodiments of transceivercircuits may be used.

Antenna or antenna array 110 may be any antenna or antenna array. Forexample, in some embodiments, antenna or antenna array 110 includes 1,2, 3, 4, or more antennas. In some embodiments, antenna or antenna array110 includes a linear antenna array. In some embodiments, antenna orantenna array 110 includes a two dimensional antenna array, for example,having multiple rows of linear antenna arrays.

In embodiments where antenna or antenna array 110 includes one antenna,the one antenna may be connected directly to transmitter RF chain 130and receiver RF chain 230, and switch 120 may be omitted. In embodimentswhere antenna or antenna array 110 includes multiple antennas, eachantenna may be directly connected to a separate receiver RF chain. Eachof the receiver RF chains may have the features of receiver RF chain130. In embodiments where antenna or antenna array 110 includes multipleantennas, each antenna may be directly connected to a separatetransmitter RF chain. Each of the transmitter RF chains may have thefeatures of transmitter RF chain 230.

Antenna or antenna array 110 may be configured to transmit RF signals toa receiver circuit, such as receiver circuit 200, or to anothertransceiver circuit. The RF signals include a high frequency signal at acarrier frequency modulated with a low frequency information signal. Thehigh frequency signal is transmitted by one of the antennas from antennaor antenna array 110, for example, according to a programmableelectrical connection formed by switch 120, as controlled by controller140.

Controller 140 is configured to provide a digital signal to RF chain130, where the digital signal encodes the information signal to betransmitted by antenna or antenna array 110.

RF chain 130 includes digital to analog converter (DAC) 132,bidirectional mixer 336, frequency synthesizer 334, and power amplifier(PA) 138. RF chain 130 is an example only, and embodiments of other RFchains may alternatively be used. For example, in some embodiments, oneor more amplifiers, and/or filters may be included, as understood bythose of skill in the art.

The digital signal is processed by the digital to analog converter 132to generate an analog baseband signal (BB signal) representing thedigital signal, using techniques known in the art. Various digital toanalog converter structures known in the art may be used.

Bidirectional mixer 336 receives the analog baseband signal output fromthe digital to analog converter 132 and an oscillator signal at thecarrier frequency generated by frequency synthesizer 334. In response tothe analog baseband signal and the oscillator signal, bidirectionalmixer 336 up converts the analog baseband signal from theanalog-to-digital converter 132 to a high frequency signal, usingtechniques known in the art. Various mixer structures known in the artmay be used. The resulting high frequency signal is at the carrierfrequency in this modulated so as to include the information of the lowfrequency information signal.

Power amplifier 138 is configured to receive the high frequency signal,and to drive the high frequency signal is one of the antennas fromantenna or antenna array 110, for example, according to a programmableelectrical connection formed by switch 120, as controlled by controller140. The power amplifier 138 drives the high frequency signal to one ofthe antennas using techniques known in the art. Various power amplifierstructures known in the art may be used.

As understood by those of skill in the art, using communicationconnectivity not illustrated in FIG. 2 , control signals from controller140 may control certain variable functionality of switch 120, poweramplifier 138, frequency synthesizer 134, bidirectional mixer 336, anddigital to analog converter 132, to cause transceiver circuit 300 totransmit data with RF signals, for example, as understood by those ofskill in the art.

The control signals from controller 140 may, for example, control switch120 to control which of multiple antennas RF chain 130 drives the highfrequency signal with.

In embodiments having multiple antennas each connected to one ofmultiple transmitter RF chains, controller 140 may generate controlsignals for each of the transmitter RF chains.

In embodiments where antenna or antenna array 110 includes one antenna,the one antenna may be connected directly to receiver RF chain 230, andswitch 120 may be omitted. In embodiments where antenna or antenna array110 includes multiple antennas, each antenna may be directly connectedto a separate receiver RF chain. Each of the receiver RF chains may havethe features of receiver RF chain 230.

Antenna or antenna array 110 may be configured to receive RF signalsgenerated by a transmitter, such as transmitter 100 or from anothertransceiver circuit.

RF chain 230 includes low noise amplifier (LNA) 232, frequencysynthesizer 334, bidirectional mixer 336, and analog to digitalconverter (ADC) 238. RF chain 230 is an example only, and embodiments ofother RF chains may alternatively be used. For example, in someembodiments, one or more amplifiers, and/or filters may be included, asunderstood by those of skill in the art.

Low noise amplifier 232 is configured to receive a high frequency signalat a carrier frequency and modulated with a low frequency informationsignal. The high frequency signal is received from one of the antennasfrom antenna or antenna array 110, for example, according to aprogrammable electrical connection formed by switch 120, as controlledby controller 140. The high frequency signal is amplified by low noiseamplifier 232 to generate an amplified RF signal, using techniques knownin the art. Various low noise amplifier structures known in the art maybe used.

Bidirectional mixer 336 receives the amplified RF signal output from thelow noise amplifier 232 and an oscillator signal at or substantially atthe carrier frequency generated by frequency synthesizer 334. Inresponse to the amplified RF signal and the oscillator signal,bidirectional mixer 336 down converts the amplified RF signal from thelow noise amplifier 232 to a baseband signal, using techniques known inthe art. Various mixer structures known in the art may be used. Theresulting baseband signal includes information of the low frequencyinformation signal.

The baseband signal is then processed by the analog-to-digital converter238 to generate a digital signal representing the baseband signal, usingtechniques known in the art. Various analog-to-digital converterstructures known in the art may be used.

Controller 140 receives the digital representation of the basebandsignal.

As understood by those of skill in the art, using communicationconnectivity not illustrated in FIG. 2 , control signals from controller240 may control certain variable functionality of switch 120, low noiseamplifier 232, frequency synthesizer 334, bidirectional mixer 336, andanalog-to-digital converter 238, to cause transceiver circuit 300 toreceive data from RF signals, for example, as understood by those ofskill in the art.

The control signals from controller 140 may, for example, control switch120 to select which of multiple antennas receiver RF chain 230 receivesthe high frequency signals from.

For example, controller 140 may generate control signals which result incontroller 140 receiving a group of digital signals, where each digitalsignal of the group is generated by receiver RF chain 230 based on ahigh frequency signal received by a selected one of the antennas. Inembodiments having multiple antennas each connected to one of multiplereceiver RF chains, controller 140 may generate control signals for eachof the receiver RF chains, such that controller 140 receives a group ofdigital signals, where each digital signal of the group is generated byone of the receiver RF chains based on an RF signal received by theparticular antenna connected thereto.

FIG. 3 is schematic diagram of a system 350 having first and secondtransceiver circuits 310 and 320 communicating wirelessly.Instantiations of transceiver circuit 300 may be used as either or bothof first and second transceiver circuits 310 and 320. Each of first andsecond transceiver circuits 310 and 320 may have features similar oridentical to that of transceiver circuit 300, discussed with referenceto FIG. 2 . Other transceiver circuits may be used as either or both offirst and second transceiver circuits 310 and 320.

In some embodiments, it may be advantageous for first transceivercircuit 310 to determine a distance between first and second transceivercircuits 310 and 320. Additionally or alternatively, it may beadvantageous for second transceiver circuit 320 to determine a distancebetween first and second transceiver circuits 310 and 320.

Three methods for distance estimation may be used: Received SignalStrength Indicator (RSSI)-based, time-based, and phase-basedmeasurements.

In RSSI-based methods, the receiver of the signal will calculate itsdistance to the transmitter based on the attenuation of the transmittedsignal over the distance. RSSI-based solutions are very sensitive tomultipath fading and other environmental influences such as humidity. Insome time-based solutions, the transit time of the signal may bemeasured directly. Therefore, these methods require highly synchronizedclocks to calculate the time between departure and arrival which isimpossible in many systems. Moreover, time-based solutions may use alarge signal bandwidth in order to have acceptable accuracy in multipathenvironments, which is incompatible with many narrowband technologiessuch as Bluetooth Low-Energy (BLE).

In phase-based methods, the amount of signal-phase shifts betweentransmitter and receiver may be used to calculate the distance betweenthem. In order to mitigate the error due to multipath problem, the phasechanges may be measured over multiple frequencies to calculate thedistance between them. This procedure is called Multi-Carrier PhaseDifference (MCPD). For the MCPD distance estimation, two roles aredefined:

-   -   Initiator: The device that starts the estimation procedure.    -   Reflector: The device that responds to the initiator.

Based on how initiator and reflector interact, there are at least twodifferent ways to implement MCPD: One-Way and Two-Way.

One-Way MCPD: The initiator sends continuous Wave (CW) signals toReflector across the frequency band of interest with a predefinedfrequency step. The received signals at the reflector are used toestimate the distance between the two devices. This method has errorsrelated to phase incoherency over the whole frequency band of interest.

Two-Way MCPD: The initiator and reflector exchange CW signals atdifferent frequencies across the frequency band of interest in a backand forth ping pong fashion. This method has errors related to phaseincoherency only over each individual ping pong communication frominitiator to reflector and vice versa, rather than over the wholefrequency band of interest.

In the discussion below, the example embodiments illustrate Two-Way MCPD(TWMCPD) method. As understood by those of skill in the art, theprinciples may also be applied to one-way MCPD.

The TWMCPD method may have three main stages:

Frequency sweep: Initiator and reflector send CW signals to each otherat different channel frequencies across the frequency band of interest.

Data transfer (IQ samples transfer): The reflector sends all itsreceived IQ samples back to the initiator.

Distance Estimation: The initiator uses the data to estimate thedistance.

Carrier frequency offset (CFO) affects the accuracy in the distanceestimation, as outlined below.

The following notation is used:

-   -   The distance or range between the initiator and the reflector is        r.    -   The initiator has crystal offset of μ_(i).    -   The reflector has crystal offset of μ_(r).    -   The phase difference between the LO signal of the initiator and        the reflector at the start of ranging procedure is θ₀.    -   The time offset between the initiator and the reflector at the        start of ranging procedure is Δt.    -   The delay between the transmitted and received tones by the        reflector is T₀.    -   ΔT₀ is the variation in T₀ between different signal exchanges.    -   The time difference between the tone exchange in channel f_(k)        and the tone exchange in the next channel f_(k)+1 is T_(f).    -   At least because of CFO, there is a frequency offset of F        between initiator and reflector.

The Initiator transmits a CW, to the reflector on the first channel, f₀.The reflector then performs I/Q measurement on the received carrier,where Δt is a time-offset between the initiator and reflector, the phaseof the received CW at the reflector is

${{\varphi_{R}\left( {f_{0},r} \right)} = {{2{\pi\left( {1 + \mu_{i}} \right)}{f_{0}\left( {\frac{r}{C} - {\Delta t}} \right)}} - {\theta_{0}\left( {{mod}2\pi} \right)}}},$

Where θ₀ is the phase difference between the LO signal of the initiatorand LO signal of the reflector at the start of the ranging procedure.

Following this, the reflector sends back a CW on the same channel, tothe initiator. At the initiator, the phase of the received signal is

${{\varphi_{I}\left( {f_{0},r} \right)} = {{2{\pi\left( {1 + \mu_{r}} \right)}\left( {f_{0} + F} \right)\left( {\frac{r}{C} + {\Delta t}} \right)} + \theta_{0} + {\theta_{0}^{\prime}\left( {{mod}2\pi} \right)}}},$Where θ₀^(′) = 2π[(1 + μ_(r))(f₀ + F) − (1 + μ_(i))(f₀)]T₀,

The initiator sums up the two phases (using its own IQ samples and theIQ samples sent from the reflector):

${\varphi_{I + R}\left( {f_{0},r} \right)} = {{4\pi f_{0}\frac{r}{C}} + {2{\pi\left( {\mu_{i} + \mu_{r}} \right)}f_{0}\frac{r}{C}} + {2\pi{F\left( {\frac{r}{C} + {\Delta t}} \right)}} + {2{\pi\mu}_{r}F\frac{r}{C}} + {2{\pi\Delta}{t\left( {{\mu_{r}\left( {f_{0} + F} \right)} - {\mu_{i}f_{0}}} \right)}} + {\theta_{0}^{\prime}\left( {{mod}2\pi} \right)}}$

This equation can be used to estimate the range, but because of thehalf-wavelength ambiguity, the maximum range

$\left( \frac{C}{2f_{0}} \right)$

is very small. In order to resolve this issue, this method isimplemented at two or more frequencies and results are then subtracted.

For a second frequency,

${\varphi_{R}\left( {f_{1},r} \right)} = {{2{\pi\left( {1 + \mu_{i}} \right)}{f_{1}\left( {\frac{r}{C} - {\Delta t} - {\left( {\mu_{r} - \mu_{i}} \right)T_{f}}} \right)}} - {\theta_{1}\left( {{mod}2\pi} \right)}}$${\varphi_{I}\left( {f_{1},r} \right)} = {{2{\pi\left( {1 + \mu_{r}} \right)}\left( {f_{1} + F} \right)\left( {\frac{r}{C} + {\Delta t} + {\left( {\mu_{r} - \mu_{i}} \right)T_{f}}} \right)} + \theta_{1} + {\theta_{1}^{\prime}\left( {{mod}2\pi} \right)}}$Where θ₁^(′) = 2π[(1 + μ_(r))(f₁ + F) − (1 + μ_(i))(f₁)](T₀ + ΔT₀)

The phase φ_(1+R) for the second frequency is:

${\varphi_{I + R}\left( {f_{1},r} \right)} = {{4\pi f_{1}\frac{r}{C}} + {2{\pi\left( {\mu_{i} + \mu_{r}} \right)}f_{1}\frac{r}{C}} + {2\pi{F\left( {\frac{r}{C} + {\Delta t} + {\left( {\mu_{r} - \mu_{i}} \right)T_{f}}} \right)}} + {2{\pi\mu}_{r}F\frac{r}{C}} + {2{\pi\left( {{\Delta t} + {\left( {\mu_{r} - \mu_{i}} \right)T_{f}}} \right)}\left( {{\mu_{r}\left( {f_{1} + F} \right)} - {\mu_{i}f_{1}}} \right)} + {\theta_{1}^{\prime}\left( {{mod}2\pi} \right)}}$

Accordingly:

${\Delta\varphi} = {{{\varphi_{I + R}\left( {f_{1},r} \right)} - {\varphi_{I + R}\left( {f_{0},r} \right)}} = {{\frac{4{\pi\Delta}f}{C}r} + {2{\pi\Delta}{f\left( {\mu_{i} + \mu_{r}} \right)}\frac{r}{C}} + {2{\pi\Delta}{t\left( {\mu_{r} - \mu_{i}} \right)}\Delta f} + {2{\pi\left( {\mu_{r} - \mu_{i}} \right)}{T_{f}\left( {{\left( {1 + \mu_{r}} \right)F} + {\left( {\mu_{r} - \mu_{i}} \right)f_{1}}} \right)}} + {2{\pi\left( {\mu_{r} - \mu_{i}} \right)}\Delta{fT}_{0}} + {2{\pi\left\lbrack {{\left( {\mu_{r} - \mu_{i}} \right)f_{1}} + {\left( {1 + \mu_{r}} \right)F}} \right\rbrack}\Delta T_{0}}}}$

and the estimated range is:

$\hat{r} = {\frac{C}{4{\pi\Delta}f}{{\Delta\varphi}\left( {{mod}\frac{C}{2\Delta f}} \right)}}$

Therefore, the ambiguity will depend on the frequency difference of bothtones.

The estimation error is:

$e = {{r - \hat{r}} = {0.5{C\left\lbrack {{\left( {\mu_{i} + \mu_{r}} \right)\frac{r}{C}} + {\Delta{t\left( {\mu_{r} - \mu_{i}} \right)}} + {\left( {\mu_{r} - \mu_{i}} \right)\left( {{\left( {1 + \mu_{r}} \right)\frac{F}{\Delta f}} + {\left( {\mu_{r} - \mu_{i}} \right)\frac{f_{1}}{\Delta f}}} \right)T_{f}} + {\left( {\mu_{r} - \mu_{i}} \right)T_{0}} + {\left( {{\left( {1 + \mu_{r}} \right)\frac{F}{\Delta f}} + {\left( {\mu_{r} - \mu_{i}} \right)\frac{f_{1}}{\Delta f}}} \right)\Delta T_{0}}} \right\rbrack}}}$

The error due to CFO is:

${{Error}{due}{to}CFO} = {{0.5{C\left\lbrack {{\left( {\mu_{r} - \mu_{i}} \right)\left( {\left( {1 + \mu_{r}} \right)\frac{F}{\Delta f}} \right)T_{f}} + {\left( {\left( {1 + \mu_{r}} \right)\frac{F}{\Delta f}} \right)\Delta T_{0}}} \right\rbrack}} \approx {0.5C\frac{F}{\Delta f}\Delta T_{0}}}$

Considering that it is near impossible to make ΔT₀ zero, for example, inBLE systems ΔT₀ is in the order of 1 μs, F results in significant error.As an example for ΔT₀=0.5 μs and Δf=2 MHz, the CFO of 50 KHz results inan estimation error of 1.875 meters.

FIG. 4 is a flowchart diagram illustrating a TWMCPD method 400 ofdetermining a distance between first and second transceivers accordingto some embodiments. Method 400 may be performed by first and secondtransceiver circuits 310 and 320.

At 405, in response to determining that a distance between the first andsecond transceiver circuits 310 and 320 is needed or desired, one of thefirst and second transceiver circuits 310 and 320 communicates with theother of first and second transceiver circuits 310 and 320. Thecommunication may request that the method of 400 be performed. Thecommunication between the first and second transceiver circuits 310 and320 identifies the one of the first and second transceiver circuits 310and 320 as the initiator and the other of the first and secondtransceiver circuits 310 and 320 as the reflector. In addition, thecommunication between the first and second transceiver circuits 310 and320 specifies the frequency band of interest and the particular channelfrequencies for the back and forth ping pong communications which willbe used for the initiator to determine the distance. The communicationmay specify other conditions for the distance determination process.

At 410, the initiator transceiver circuit transmits a first continuouswave or other signal as a first initiation signal to the to thereflector transceiver circuit at a first working frequency of thefrequency band of interest. In some embodiments, either or both of thefirst working frequency and the frequency band of interest werecommunicated at 405. In some embodiments, either or both of the firstworking frequency and the frequency band of interest are specified by acommunications standard.

At 415, the reflector transceiver circuit receives the first continuouswave or other signal from the initiator transceiver circuit at the firstworking frequency. In addition, the reflector transceiver circuitestimates the carrier frequency offset (CFO). Any method of CFOestimation may be used. For example, the reflector transceiver circuitmay find a phase difference between two points of a signal with knowntime difference, and determine a frequency based on the phasedifference, where the frequency=(phase difference)/(2*pi*timedifference).

At 415, the reflector transceiver circuit also performs I/Q measurementon the received continuous wave or other signal using the CFO estimateof 415 to compensate for the CFO of the communication.

At 420, the reflector transceiver circuit transmits a second continuouswave or other signal as a first reflection signal to the initiatortransceiver circuit at the first working frequency of the frequency bandof interest.

In some embodiments, a frequency synthesizer controlling the workingfrequency for both the receive action of 415 and the transmit action of420 is set before 415 and is not reset between 415 and 420. Accordingly,a locking circuit, such as a PLL or a DLL, of the frequency synthesizermay be locked before 415 and remain locked throughout 415 and 420.

At 425, the initiator transceiver circuit receives the second continuouswave or other signal from the reflector transceiver circuit at the firstworking frequency. In addition, the initiator transceiver circuitestimates the carrier frequency offset (CFO). Any method of CFOestimation may be used. At 425, the initiator transceiver circuit alsoperforms I/Q measurement on the received continuous wave or other signalusing the estimated CFO to compensate for the CFO in the communication.

In some embodiments, a frequency synthesizer controlling the workingfrequency for both the transmit action of 410 and the receive action of425 is set before 410 and is not reset between 410 and 425. Accordingly,a locking circuit, such as a PLL or a DLL, of the frequency synthesizermay be locked before 410 remain locked throughout 410 and 425.

In some embodiments, the order of operations is different. For example,in some embodiments, 420 occurs after 405, 425 occurs after 420, 410occurs after 425, 415 occurs after 410, and 430 occurs after 415.

At 430, if another working frequency of the frequency band of interestis to be used, at 435, the working frequency is changed, and the method400 returns to 410. Any total number of working frequencies may be used.

Otherwise, if another working frequency of the frequency band ofinterest is not to be used, at 440, the reflector transceiver circuittransmits data representing the FQ measurements made at all occurrencesof 415 to the initiator transceiver circuit. The working frequency ofthe transmission may be the last working frequency used at 410, 415,420, and 425. In some embodiments, the working frequency of thetransmission is another frequency, for example, of the frequency band ofinterest. The other frequency may have been communicated at 405. In someembodiments, the other frequency is specified by a communicationsstandard.

At 445, the initiator transceiver circuit receives the data transmittedby the reflector transceiver circuit at 440. The initiator transceivercircuit receives the data transmitted from the reflector transceivercircuit at the working frequency. In addition, the initiator transceivercircuit estimates the carrier frequency offset (CFO). Any method of CFOestimation may be used. At 445, the initiator transceiver circuit alsoperforms FQ measurement on the received transmission using the estimatedCFO to compensate for the CFO in the communication.

At 450, the initiator transceiver circuit estimates the distance betweenthe initiator transceiver circuit and the reflector transceiver circuitbased on the I/Q data received from the reflector transceiver circuit at445 and generated at the occurrences of 425. For example, the distancemay be estimated according to the equation shown above:

$\hat{r} = {\frac{C}{4\pi\Delta f}{{\Delta\varphi}\left( {{mod}\frac{C}{2\Delta f}} \right)}}$

FIG. 5 is a schematic diagram representing the actions of the first andsecond transceivers performing certain portions of the method of FIG. 4according to some embodiments.

As illustrated, first and second signal exchanges are represented, whereeach signal exchange includes:

-   -   the initiator circuit transmitting a 1^(st) signal at a working        frequency, at 410;    -   the reflector circuit receiving the 1^(st) signal at the working        frequency, at 415;    -   after a time T₀,    -   the reflector circuit transmitting a 2^(nd) signal at the        working frequency, at 420; and    -   the initiator circuit receiving the 2^(nd) signal at the working        frequency, at 425.

As illustrated, the working frequency of the first signal exchange 1 isfc, and the working frequency of the second signal exchange 2 is fc+Δf.In addition, FIG. 5 illustrates that the second signal exchange 2happens a time T_(f) after the first signal exchange 1, where duringtime T_(f), the working frequency of the initiator circuit and thereflector circuit is changed from fc to fc+Δf, at 435.

FIG. 6 is a flowchart diagram illustrating a TWMCPD method 600 ofdetermining a distance between first and second transceivers accordingto some embodiments. Method 600 may be performed by first and secondtransceiver circuits 310 and 320.

At 605, in response to determining that a distance between the first andsecond transceiver circuits 310 and 320 is needed or desired, one of thefirst and second transceiver circuits 310 and 320 communicates with theother of first and second transceiver circuits 310 and 320. Thecommunication may request that the method of 600 be performed. Thecommunication between the first and second transceiver circuits 310 and320 identifies the one of the first and second transceiver circuits 310and 320 as the initiator and the other of the first and secondtransceiver circuits 310 and 320 as the reflector. In addition, thecommunication between the first and second transceiver circuits 310 and320 specifies the frequency band of interest and the particular channelfrequencies for the back and forth ping pong communications which willbe used for the initiator to determine the distance. The communicationmay specify other conditions for the distance determination process.

At 608, a CFO estimate is made. Any method of CFO estimation may beused. For example, method 400 may be used to determine the CFO estimate.In some embodiments, the CFO estimate is made as part of one or morecommunications occurring as part of 605. In some embodiments, the CFOestimate is made as part of one or more communications occurring priorto 605. In some embodiments, the CFO estimate is made as part of one ormore communications occurring as part of 610 and 615, or as part of 620and 625, discussed below. In some embodiments, the CFO estimate is madeas part of one or more communications occurring as part of 610, 615, 620and 625, discussed below.

In some embodiments, the CFO estimate is made at 608 based on a singletransmission at a particular working frequency from the reflectortransceiver circuit to the initiator transceiver circuit or from theinitiator transceiver circuit to the reflector transceiver circuit. Insome embodiments, the CFO estimate is made based on a single signalexchange at a particular working frequency between the reflectortransceiver circuit and the initiator transceiver circuit, similar oridentical to either of the first and second signal exchanges illustratedin FIG. 5 .

In some embodiments, the particular working frequency used for thecommunication for the CFO estimate is the first working frequency of thesignal exchanges which include 610, 615, 620, and 625, discussed below.In some embodiments, the particular working frequency is another of theworking frequencies of the signal exchanges which include 610, 615, 620,and 625. In some embodiments, the particular working frequency is equalto or about equal to a middle frequency of the frequency band ofinterest. For example, the difference between the particular workingfrequency and the middle frequency of the frequency band of interest maybe less than 1%, 2%, 3%, 5%, 10%, 15%, or 20% of the frequency band ofinterest.

At 610, the initiator transceiver circuit transmits a first continuouswave or other signal as an initiation signal to the reflectortransceiver circuit at a first working frequency of the frequency bandof interest. In some embodiments, either or both of the first workingfrequency and the frequency band of interest were communicated at 605.In some embodiments, either or both of the first working frequency andthe frequency band of interest are specified by a communicationsstandard.

At 615, the reflector transceiver circuit receives the first continuouswave or other signal from the initiator transceiver circuit at the firstworking frequency. The reflector transceiver circuit also performs I/Qmeasurement on the received continuous wave or other signal using theCFO estimate of 608 to compensate for the CFO of the communication.

At 620, the reflector transceiver circuit transmits a second continuouswave or other signal as an reflection signal of to the initiatortransceiver circuit at the first working frequency of the frequency bandof interest.

In some embodiments, a frequency synthesizer controlling the workingfrequency for both the receive action of 615 and the transmit action of620 is set before 615 and is not reset between 615 and 620. Accordingly,a locking circuit, such as a PLL or a DLL, of the frequency synthesizermay be set before 615 and remain locked throughout 615 and 620.

At 625, the initiator transceiver circuit receives the second continuouswave or other signal from the reflector transceiver circuit at the firstworking frequency. The initiator transceiver circuit also performs I/Qmeasurement on the received continuous wave or other signal using theCFO estimate of 608 to compensate for the CFO of the communication.

In some embodiments, a frequency synthesizer controlling the workingfrequency for both the transmit action of 610 and the receive action of625 is set before 610 and is not reset between 610 and 625. Accordingly,a locking circuit, such as a PLL or a DLL, of the frequency synthesizermay be locked before 610 and remain locked throughout 610 and 625.

In some embodiments, the order of operations is different. For example,in some embodiments, 620 occurs after 605, 625 occurs after 620, 610occurs after 625, 615 occurs after 610, and 630 occurs after 615.

At 630, if another working frequency of the frequency band of interestis to be used, at 635, the working frequency is changed, and the method600 returns to 610. Any total number of working frequencies may be used.

Otherwise, if another working frequency of the frequency band ofinterest is not to be used, at 640, the reflector transceiver circuittransmits data representing the I/Q measurements made at all occurrencesof 615 to the initiator transceiver circuit. The working frequency ofthe transmission may be the last working frequency used at 610, 615,620, and 625. In some embodiments, the working frequency of thetransmission is another frequency, for example, of the frequency band ofinterest. The other frequency may have been communicated at 605. In someembodiments, the other frequency is specified by a communicationsstandard.

At 645, the initiator transceiver circuit receives the data transmittedby the reflector transceiver circuit at 640. The initiator transceivercircuit may receive the data transmitted from the reflector transceivercircuit at the working frequency. The initiator transceiver circuit alsoperforms I/Q measurement on the received transmission. In someembodiments, initiator transceiver circuit also performs I/Q measurementon the received transmission using the CFO estimate of 608 to compensatefor the CFO in the communication. In some embodiments, initiatortransceiver circuit also performs I/Q measurement on the receivedtransmission using another CFO estimate to compensate for the CFO in thecommunication.

At 650, the initiator transceiver circuit estimates the distance betweenthe initiator transceiver circuit and the reflector transceiver circuitbased on the I/Q data received from the reflector transceiver circuit at645 and generated at the occurrences of 625. Any method of estimatingthe distance may be used. For example, any methods of estimating thedistance discussed herein may be used.

FIG. 7 is a schematic diagram representing the actions of the first andsecond transceivers performing certain portions of the method of FIG. 6according to some embodiments.

As illustrated, CFO estimation 608 is represented, where, in thisembodiment, CFO estimation 608 includes:

-   -   the initiator circuit transmitting a 1^(st) signal;    -   the reflector circuit receiving the 1^(st) signal;    -   the reflector circuit transmitting a 2^(nd) signal; and    -   the initiator circuit receiving the 2^(nd) signal.

As illustrated, first and second signal exchanges are represented, whereeach signal exchange includes:

-   -   the initiator circuit transmitting a 1^(st) signal at a working        frequency, at 610;    -   the reflector circuit receiving the 1^(st) signal at the working        frequency, at 615;    -   after a time T₀,    -   the reflector circuit transmitting a 2^(nd) signal at the        working frequency, at 620; and    -   the initiator circuit receiving the 2^(nd) signal at the working        frequency, at 625.

As illustrated, the working frequency of the first signal exchange 1 isfc, and the working frequency of the second signal exchange 2 is fc+Δf.In addition, FIG. 7 illustrates that the second signal exchange 2happens a time T_(f) after the first signal exchange 1, where duringtime T_(f), the working frequency of the initiator circuit and thereflector circuit is changed from fc to fc+Δf.

FIG. 8 is a flowchart diagram illustrating a TWMCPD method 800 ofdetermining a distance between first and second transceivers accordingto some embodiments. Method 800 may be performed by first and secondtransceiver circuits 310 and 320.

At 805, in response to determining that a distance between the first andsecond transceiver circuits 310 and 320 is needed or desired, one of thefirst and second transceiver circuits 310 and 320 communicates with theother of first and second transceiver circuits 310 and 320. Thecommunication may request that the method of 800 be performed. Thecommunication between the first and second transceiver circuits 310 and320 identifies the one of the first and second transceiver circuits 310and 320 as the initiator and the other of the first and secondtransceiver circuits 310 and 320 as the reflector. In addition, thecommunication between the first and second transceiver circuits 310 and320 specifies the frequency band of interest and the particular channelfrequencies for the back and forth ping pong communications which willbe used for the initiator to determine the distance. The communicationmay specify other conditions for the distance determination process.

At 810, the initiator transceiver circuit transmits a first continuouswave or other signal as an initiation signal to the reflectortransceiver circuit at a first working frequency of the frequency bandof interest. In some embodiments, either or both of the first workingfrequency and the frequency band of interest were communicated at 805.In some embodiments, either or both of the first working frequency andthe frequency band of interest are specified by a communicationsstandard.

At 815, the reflector transceiver circuit receives the first continuouswave or other signal from the initiator transceiver circuit at the firstworking frequency. In addition, the reflector transceiver circuitestimates the carrier frequency offset (CFO). Any method of CFOestimation may be used. For example, the reflector transceiver circuitmay find a phase difference between two points of a signal with knowntime difference, and determine a frequency based on the phasedifference, where the frequency=(phase difference)/(2*pi*timedifference).

At 815, the reflector transceiver circuit also performs I/Q measurementon the received continuous wave or other signal using the CFO estimateof 815 to compensate for the CFO of the communication. In addition, thereflector transceiver circuit also saves the CFO estimate and the I/Qmeasurement data of 815 in a memory so it can be used later, asdescribed below with reference to 848.

At 820, the reflector transceiver circuit transmits a second continuouswave or other signal as an reflection signal to the initiatortransceiver circuit at the first working frequency of the frequency bandof interest.

In some embodiments, a frequency synthesizer controlling the workingfrequency for both the receive action of 815 and the transmit action of820 is set before 815 and is not reset between 815 and 820. Accordingly,a locking circuit, such as a PLL or a DLL, of the frequency synthesizermay be set before 815 and remain locked throughout 815 and 820.

At 825, the initiator transceiver circuit receives the second continuouswave or other signal from the reflector transceiver circuit at the firstworking frequency. In addition, the initiator transceiver circuitestimates the carrier frequency offset (CFO). Any method of CFOestimation may be used.

In some embodiments, a frequency synthesizer controlling the workingfrequency for both the transmit action of 810 and the receive action of825 is set before 810 and is not reset between 810 and 825. Accordingly,a locking circuit, such as a PLL or a DLL, of the frequency synthesizermay be locked before 810 and remain locked throughout 810 and 825.

At 825, the initiator transceiver circuit also performs I/Q measurementon the received continuous wave or other signal using the CFO estimateof 825 to compensate for the CFO of the communication. In addition, thereflector transceiver circuit also saves the CFO estimate and the I/Qmeasurement data of 825 in a memory so it can be used later, asdescribed below with reference to 848.

In some embodiments, the order of operations is different. For example,in some embodiments, 820 occurs after 805, 825 occurs after 820, 810occurs after 825, 815 occurs after 810, and 830 occurs after 815.

At 830, if another working frequency of the frequency band of interestis to be used, at 835, the working frequency is changed, and the method800 returns to 810. Any total number of working frequencies may be used.

Otherwise, if another working frequency of the frequency band ofinterest is not to be used, at 838, the reflector transceiver circuitmodifies the I/Q data generated in the FQ measurements at theoccurrences of 815. In accordance with that discussed above, in someembodiments, the I/Q data generated in the I/Q measurements at theoccurrences of 815 was generated using CFO estimates specific to thecommunications which were used to generate the FQ measurements.

To modify the I/Q data generated at the occurrences of 815, thereflector transceiver circuit removes the effect of those specific CFOestimates from the I/Q data. In some embodiments, to remove the effectof the CFO estimates from the FQ data generated at the occurrences of815, the reflector transceiver circuit may multiply each of the I/Q datameasurements r_(n)(t) generated at the occurrences of 815 by exp(2 π iF′_(n) t) to generate uncompensated reflector I/Q measurements, where tis the sample time, and F′_(n) is the CFO estimate used to generater_(n)(t).

At 840, the reflector transceiver circuit transmits data representingthe uncompensated reflector I/Q measurements made at all occurrences of815 to the initiator transceiver circuit. The working frequency of thetransmission may be the last working frequency used at 810, 815, 820,and 825. In some embodiments, the working frequency of the transmissionis another frequency, for example, of the frequency band of interest.The other frequency may have been communicated at 805. In someembodiments, the other frequency is specified by a communicationsstandard.

At 845, the initiator transceiver circuit receives the data transmittedby the reflector transceiver circuit at 840. The initiator transceivercircuit receives the data transmitted from the reflector transceivercircuit at the working frequency.

At 848, the initiator transceiver circuit modifies the I/Q datagenerated at the occurrences of 825. In accordance with that discussedabove, in some embodiments, the I/Q data generated at the occurrences of825 was generated using CFO estimates specific to the communicationswhich were used to generate the I/Q measurements.

To modify the I/Q data generated at the occurrences of 825, theinitiator transceiver circuit removes the effect of the CFO estimatesfrom the I/Q data generated at the occurrences of 825.

In some embodiments, to remove the effect of the CFO estimates from theI/Q data generated at the occurrences of 825, the initiator transceivercircuit may multiply each of the I/Q data measurements r_(n)(t)generated at the occurrences of 825 by exp(2 π i F′_(n) t) to generateuncompensated initiator I/Q measurements, where t is the sample time,and F′_(n) is the CFO estimate used to generate r_(n)(t).

In some embodiments, the initiator transceiver circuit, at 848, alsoincludes the effect of a single CFO estimate on the uncompensatedreflector I/Q measurements received at 845 and on the uncompensatedinitiator I/Q measurements. To include the effect of the single CFOestimate on the uncompensated reflector and initiator I/Q measurements,the initiator transceiver circuit may multiply each of the uncompensatedI/Q data measurements by exp(−2 π i F t), to generate modified I/Q data,where F is the single CFO estimate.

The single CFO estimate may be a particular one of the CFO estimates ofthe I/Q data received from the reflector transceiver circuit at 845 andgenerated at the occurrences of 825. In some embodiments, the single CFOestimate may be an average of the CFO estimates of the I/Q data receivedfrom the reflector transceiver circuit at 845 and generated at theoccurrences of 825.

In some embodiments, the initiator transceiver circuit includes theeffect of a first CFO estimate on the uncompensated reflector I/Qmeasurements, and includes the effect of a second CFO estimate on theuncompensated initiator I/Q measurements.

To include the effect of the first CFO estimate on the uncompensatedreflector I/Q measurements, the initiator transceiver circuit maymultiply each of the uncompensated reflector I/Q measurements by exp(−2π i F₁ t), to generate modified reflector I/Q data, where F₁ is thefirst CFO estimate. The first CFO estimate may be a CFO estimatereceived from the reflector transceiver circuit, for example, at 845. Insome embodiments, the first CFO estimate may be a particular one of theCFO estimates generated by the reflector transceiver circuit at one ofthe occurrences of 815. In some embodiments, the first CFO estimate maybe an average of the CFO estimates generated by the reflectortransceiver circuit at the occurrences of 815. In some embodiments, thefirst CFO estimate is another CFO estimate.

In some embodiments, to include the effect of a second CFO estimate onthe uncompensated initiator I/Q measurements generated at 848, theinitiator transceiver circuit may multiply each of the uncompensatedinitiator I/Q measurements by exp(−2 π i F₂ t), to generate modifiedinitiator I/Q data, where F₂ is the second CFO estimate. The second CFOestimate may be a particular one of the CFO estimates generated at theoccurrences of 825. In some embodiments, the second CFO estimate may bean average of the CFO estimates generated at the occurrences of 825. Insome embodiments, the first CFO estimate is another CFO estimate.

At 850, the initiator transceiver circuit estimates the distance betweenthe initiator transceiver circuit and the reflector transceiver circuitbased on the modified initiator and reflector I/Q measurements. Anymethod of estimating the distance may be used. For example, any methodsof estimating the distance discussed herein may be used.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it used, such a phrase is intendedto mean any of the listed elements or features individually or any ofthe recited elements or features in combination with any of the otherrecited elements or features. For example, the phrases “at least one ofA and B;” “one or more of A and B;” and “A and/or B” are each intendedto mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” Use of the term “based on,” above and in theclaims is intended to mean, “based at least in part on,” such that anunrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and subcombinations of the disclosed featuresand/or combinations and subcombinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

What is claimed is:
 1. A transceiver circuit, comprising: an antenna; areceiver RF chain configured to receive a receiver RF signal from theantenna; a transmitter RF chain configured to transmit a transmitter RFsignal to the antenna; and a controller configured to access a CFO(carrier frequency offset) estimate, and to, for each of one or moreworking frequencies: cause the receiver RF chain to receive a receiverRF signal from the antenna at each working frequency, generate I/Qmeasurement data based at least in part on the received receiver RFsignal and the CFO estimate, store the I/Q measurement data, and causethe transmitter RF chain to transmit a transmitter RF signal to theantenna at each working frequency, wherein the controller is furtherconfigured to cause the transmitter RF chain to transmit the I/Qmeasurement data for each working frequency to the antenna.
 2. Thetransceiver circuit of claim 1, further comprising a frequencysynthesizer configured to control the working frequency, wherein thecontroller is configured to cause the frequency synthesizer to set theworking frequency to a particular working frequency before causing thereceiver RF chain to receive a particular receiver RF signal from theantenna at the particular working frequency, and wherein the controlleris configured to cause the frequency synthesizer to maintain the workingfrequency at the a particular working frequency at least until thecontroller causes the transmitter RF chain to transmit a particulartransmitter RF signal to the antenna at the particular workingfrequency.
 3. The transceiver circuit of claim 1, further comprising afrequency synthesizer configured to control the working frequency,wherein the controller is configured to cause the frequency synthesizerto set the working frequency to a particular working frequency beforecausing the transmitter RF chain to transmit a particular transmitter RFsignal to the antenna at the particular working frequency, and whereinthe controller is configured to cause the frequency synthesizer tomaintain the working frequency at the a particular working frequency atleast until the controller causes the receiver RF chain to receive aparticular receiver RF signal from the antenna at the particular workingfrequency.
 4. The transceiver circuit of claim 1, wherein the controlleris further configured to cause the receiver RF chain to receive a CFO RFsignal from the antenna at a predetermined working frequency, and togenerate the CFO estimate based at least in part on I/Q measurement dataof the CFO RF signal.
 5. The transceiver circuit of claim 4, wherein theone or more working frequencies comprises a plurality of workingfrequencies spanning a frequency band of interest, and wherein thepredetermined working frequency is about in the middle of the frequencyband of interest.
 6. The transceiver circuit of claim 1, wherein the oneor more working frequencies comprises first and second workingfrequencies, and wherein the I/Q measurement data generated based inpart on the receiver RF signals received at each of the first and secondworking frequencies are generated based in part on the same CFOestimate.
 7. The transceiver circuit of claim 1, wherein the one or moreworking frequencies comprises a plurality of working frequencies, andwherein all of the I/Q measurement data transmitted for each workingfrequency is generated based on the same CFO estimate.
 8. A transceivercircuit, comprising: one or more antennas; a receiver RF chainconfigured to receive a receiver RF signal from at least one of theantennas; a transmitter RF chain configured to transmit a transmitter RFsignal to at least one of the antennas; and a controller configured to,for each of one or more working frequencies: cause the receiver RF chainto receive a receiver RF signal, generate I/Q measurement data based atleast in part on the received receiver RF signal, and cause thetransmitter RF chain to transmit the I/Q measurement data for eachworking frequency.
 9. The transceiver circuit of claim 8, furthercomprising a frequency synthesizer configured to control the workingfrequency, wherein the controller is configured to cause the frequencysynthesizer to set the working frequency to a particular workingfrequency before causing the receiver RF chain to receive a particularreceiver RF signal at the particular working frequency, and wherein thecontroller is configured to cause the frequency synthesizer to maintainthe working frequency at the a particular working frequency at leastuntil the controller causes the transmitter RF chain to transmit aparticular transmitter RF signal at the particular working frequency.10. The transceiver circuit of claim 8, further comprising a frequencysynthesizer configured to control the working frequency, wherein thecontroller is configured to cause the frequency synthesizer to set theworking frequency to a particular working frequency before causing thetransmitter RF chain to transmit a particular transmitter RF signal atthe particular working frequency, and wherein the controller isconfigured to cause the frequency synthesizer to maintain the workingfrequency at the a particular working frequency at least until thecontroller causes the receiver RF chain to receive a particular receiverRF signal at the particular working frequency.
 11. The transceivercircuit of claim 8, wherein the controller is further configured tocause the receiver RF chain to receive a CFO RF signal at apredetermined working frequency, and to generate a CFO estimate based atleast in part on I/Q measurement data of the CFO RF signal.
 12. Thetransceiver circuit of claim 11, wherein the one or more workingfrequencies comprises a plurality of working frequencies spanning afrequency band of interest, and wherein the predetermined workingfrequency is about in the middle of the frequency band of interest. 13.The transceiver circuit of claim 8, wherein the one or more workingfrequencies comprises first and second working frequencies, and whereinthe I/Q measurement data generated based in part on the receiver RFsignals received at each of the first and second working frequencies aregenerated based in part on first and second CFO estimates, wherein thefirst and second CFO estimates are equal.
 14. The transceiver circuit ofclaim 8, wherein the one or more working frequencies comprises aplurality of working frequencies, and wherein all of the I/Q measurementdata transmitted for each working frequency is generated based on thesame CFO estimate.
 15. A transceiver circuit, comprising: a receiver RFchain configured to receive a receiver RF signal; a transmitter RF chainconfigured to transmit a transmitter RF signal; and a controllerconfigured to, for each of one or more working frequencies: cause thereceiver RF chain to receive a receiver RF signal, generate I/Qmeasurement data based at least in part on the received receiver RFsignal, and store the generated I/Q measurement data, and cause thetransmitter RF chain to transmit the stored I/Q measurement data foreach working frequency.
 16. The transceiver circuit of claim 15, furthercomprising a frequency synthesizer configured to control the workingfrequency, wherein the controller is configured to cause the frequencysynthesizer to set the working frequency to a particular workingfrequency before causing the receiver RF chain to receive a particularreceiver RF signal at the particular working frequency, and wherein thecontroller is configured to cause the frequency synthesizer to maintainthe working frequency at the a particular working frequency at leastuntil the controller causes the transmitter RF chain to transmit aparticular transmitter RF signal at the particular working frequency.17. The transceiver circuit of claim 15, further comprising a frequencysynthesizer configured to control the working frequency, wherein thecontroller is configured to cause the frequency synthesizer to set theworking frequency to a particular working frequency before causing thetransmitter RF chain to transmit a particular transmitter RF signal atthe particular working frequency, and wherein the controller isconfigured to cause the frequency synthesizer to maintain the workingfrequency at the a particular working frequency at least until thecontroller causes the receiver RF chain to receive a particular receiverRF signal at the particular working frequency.
 18. The transceivercircuit of claim 15, wherein the controller is further configured tocause the receiver RF chain to receive a CFO RF signal at apredetermined working frequency, and to generate a CFO estimate based atleast in part on I/Q measurement data of the CFO RF signal.
 19. Thetransceiver circuit of claim 18, wherein the one or more workingfrequencies comprises a plurality of working frequencies spanning afrequency band of interest, and wherein the predetermined workingfrequency is about in the middle of the frequency band of interest. 20.The transceiver circuit of claim 15, wherein the one or more workingfrequencies comprises first and second working frequencies, and whereinthe I/Q measurement data generated based in part on the receiver RFsignals received at each of the first and second working frequencies aregenerated based in part on first and second CFO estimates, wherein thefirst and second CFO estimates are equal.